AM radio

You'll risk more birdies if you put the local oscillator below the desired input frequency. With your scheme, you need to attenuate 800 kHz before mixing.

The ARRL Handbooks have changed quite a lot in 19 years. Have a look at the current one.

--

Tauno Voipio

--
That may be true, but it's not the image frequency.

The image is a frequency located at RF + 2IF if the LO is injected
above the carrier frequency, and RF - 2IF if it's injected below the
carrier.

For example, an AM station located at 1000 kHz is tuned to using a
receiver with a 455 kHz IF. 

The LO is tuned to 1000+455 = 1455 kHz, but a signal at 
1000+455+455=1910 kHz is also 455 kHz away from the local oscillator,
so both the desired signal and the image, when mixed with the local
oscillator, will appear at the IF.

--
Yes, I know.

You seem to have changed your mind though, since you earlier posted
this:

You: 

"You'll have zero image rejection, which is educational in itself."

George Herold:

"Umm,  can you tell me what that means?  (Or some wiki page that talks
about it.)"

You:

"It means that there are two LO frequencies that will receive any
given AM station. So in some cases, stations will overlap at one LO
setting, but you can separate out one of them at some other LO
frequency."

I don't recall changing my mind on anything here. This is basic EE stuff.

John

--
Short attention span?

In the first place you told George Herold that zero image rejection
meant that two LOs could be used to tune to the same station, which is
true, but has little to do with image rejection.

Then when I challenged you on your error you replied with the correct
answer.
 
How is that _not_ changing your mind?

into

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Without a preselector filter, a superhet will receive two different frequencies at any given LO setting. Or you can use two different LO settings to receive a given frequency. That's the math. It's all the same thing.

Which frequency is the "image" depends on which station you feel like listening to.

John

into

of

It's exactly the same thing. One LO receives two stations, and there are two LO frequencies that will receive any given station. And a preselect bandpass filter supresses both effects.

Error? All the stuff I said was true. All you want to do is argue definitions. The math doesn't care about what words you prefer to use.

Damn, but you're a prissy and tedious old idiot.

John

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--
Yeah, but so what? 

All you're doing is dancing around trying to pretend that you answered
George's question correctly, when you did not.

Had you answered it correctly you would have explained what an image
is and where it's located spectrally.

The 1992 Handbook is probably better. Different Handbooks approach the problems differently, with most of the older material getting washed out by new after 10 years or so.

I am surprised that the '59 handbook doesn't have a better discussion of regeneration -- usually the "detection" portion of the HB starts you off with simple diode detectors, then regeneration.

There is a lot of hand-waving, though: Handbooks are trying to not scare away an audience composed of technicians, beauticians, doctors, lawyers, auto mechanics and lumber jacks. So they do water the theory down.

--
www.wescottdesign.com

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No John, It's fine, I got it the first time. It doesn't really matter to me what it's called. And it does make it a bit more interesting.

(I'm listen to M. Jackson telling me how to 'beat it' on AM 1400 in Buffalo NY. LO tuned to 1500 (kHz.)

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Hi Tim, I took the '92 edition to lunch today. Much nicer!

I shot a picture,

I'll have to play around with the front end a bit.

Thanks again for the sage advice.

George H.

"John Larkin" wrote in message news: snipped-for-privacy@4ax.com...

Saw a circuit of one in some datasheet. Loaded with transistors -- mainly inverters. You'd think it might be reasonable to just complement all the signals coming in, do the flippy-floppy stuff, and be done, but they drew everything out with separate flops and extra inverters between them. Who knows. Sure destroyed the elegance of what should've been a very beautiful flip-flop cell.

I don't think LS logic appears in any of our power supplies, but a lot have CD4000, which is good to interface with the analog stuff, or 74AC, for the speed and noise immunity. For that matter, most of them have microcontrollers and simple displays, but ours blows them out of the water.

When I came onto this project, we had a conference with all guys who designed those machines. We told them we were using this and that low voltage FPGA and isolator chip. Usual story, they said it wouldn't work, tried it before and it didn't work.

But hey, 480V doesn't lie, and we've never had a failure of either part. For that matter, we haven't collected "buckets" of dead transistors. Careful design always pays off.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

ISTR Phil Karn (KA9Q), he who wrote the original DOS based TCP/IP NOS for the PC, being quoted as saying "The Internet has subsumed everything interesting about amateur radio".

That was about 20 years ago.

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)

Electrically short antennas have low radiation resistance (a few ohms), and a large capacitive component.

--
"For a successful technology, reality must take precedence 
over public relations, for nature cannot be fooled."
                                       (Richard Feynman)

Dual personality, or did you mean "alumnus"?

;-)

-- "For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." (Richard Feynman)

=A0 =A0(Richard Feynman)

Oh, I guess that makes sense. Can I use the DC formula for capacitance of a long wire, length L and radius R? (I want a large capacitance, I think.)

I was also wondering if I used a coil antenna, could I then use a current sensitive front end... TIA opamp?

George H.

=A0 =A0(Richard Feynman)

No we are both members. It costs more, but totally worth it to be a use the royal 'we'.

George H.

(I've already apologized once for my lack of language skills in this thread.)

Just as a note, many state universities allow residents to get a card, with various privileges, for their libraries. The rationale being that they paid for the library, they should be able to use it.